To make a styrenic polymer foam, conventional low molecular weight brominated compound such as hexabromocyclododecane (HBCD) is typically used as a flame retardant. However, HBCD is facing governmental regulation over environmental concerns. Therefore, there is a need for an alternative flame retardant for use in styrenic foam.
U.S. patent application US2008/0287559A discloses the use of a brominated vinyl aromatic/butadiene copolymer as an alternative flame retardant to HBCD in styrenic foam. A challenge with using the brominated vinyl aromatic/butadiene copolymer is that it tends to nucleate cell growth during foaming to a larger degree than HBCD due to the dispersed particulate nature of the brominated vinyl aromatic/butadiene copolymer in the polystyrene matrix. As a result an undesired amount of nucleation can occur in polystyrene foam, which produces a greater number of cells, smaller cells and a higher density foam than foam made using HBCD.
U.S. Pat. No. 4,229,396 discloses natural and synthetic waxes as a cell size enlarger of an alkenyl aromatic resin. However, there is no suggestion that polyethylene wax is able to effectively work to produce larger cells in the presence of particulates by counteracting the nucleating effect of the particles (such as brominated vinyl aromatic/butadiene copolymer particles) during the formation of a styrenic polymer foam.
Additives such as cell size enlarger affect not only cell size and density of a polymeric foam but also other properties of a polymeric composition or a polymeric foam. It causes difficulty in forming a polymeric foam. For example, during forming a polymeric foam by extruder, output speed of a foam is affected by the properties of a polymeric composition such as smoothness of the surface of the composition. Less smoothness leads hardness of extrusion, but extreme smoothness leads slip of composition and decrease the speed of extrusion. The slip of composition causes the decline of productivity and deterioration of the obtained foam. Therefore, the combination of flame retardant and additives which shows required properties for polymeric composition and polymeric foam is important.
It is desirable to find an additive that would allow preparation of HBCD-free styrenic polymer foam comprising brominated vinyl aromatic/butadiene copolymer that has a larger cell size and lower density than a comparable styrenic polymer foam prepared in the absence of the additive. It is particularly desirable to prepare such a foam where the cell size is at least as large as comparable HBCD-containing styrenic polymer foam and the density as at least as low as a comparable HBCD-containing styrenic polymer foam, without affecting smoothness of a surface of a polymeric composition.